1. Field of the Invention
The present invention relates generally to a bearing and a shaft, and more particularly to a method for manufacturing the bearing with hydrodynamic pressure generating grooves.
2. Description of Related Art
At present, hydrodynamic bearings are widely used in spindle motors in devices, such as compact disc (CD) drivers, digital video disc (DVD) drivers, hard disk drivers, laser beam printers, floppy disk drivers or in heat-dissipation fans. Spindle motors require a hydrodynamic bearing of small size, high rotational accuracy and with a long operating life.
A typical hydrodynamic bearing defines a bearing hole therein. A shaft is rotatably received in the bearing hole. A plurality of herringbone-shaped grooves are defined either in an inner circumferential surface of the bearing or in an external circumferential surface of the shaft. The grooves can accommodate lubricants such as oil. During rotation of the shaft, the lubricant is driven by the rotation of the shaft to rotate with the shaft. A lubricating film is thus formed in a clearance between the external circumferential surface of the shaft and the inner circumferential surface of the bearing. The shaft is thus supported by hydrodynamic shearing stress and dynamic pressure generated by the lubricating film when the lubricant flows through different cross-sections. However, lubricant retention and air elimination are problems in related hydrodynamic bearing devices. The lubricant is inclined to leak out because of pumping action in the hydrodynamic bearing. Accordingly, the hydrodynamic bearing cannot work normally due to lack of the lubricant. In addition, it is hard to expel air if it becomes trapped in the hydrodynamic bearing during, for example, manufacturing. Trapped air can thus cause difficulties in assembly of the related hydrodynamic bearings.
U.S. Pat. No. 5,018,880 discloses a method for defining an oil retaining groove to solve the lubricant retention and air elimination problems of the related hydrodynamic bearing. However, the small size of the hydrodynamic bearing results in difficulties particularly in the making of the oil retaining groove therein. This makes manufacturing of the hydrodynamic bearing both time-consuming and expensive. Therefore, the related method is not suitable for mass-production of the hydrodynamic bearing.
It is therefore desirable to provide an improved method for mass-production of a hydrodynamic with good functions for lubricant retention and air expelling.